Ridged shank nails are used where it is desired to preclude the nails from working loose from the boards, planks or the like into which the nails have been driven.
These nails are used for wallboard, as boat nails and as a flooring or underlayment nails, by way of example, and may conform to the German UIC commercial standard 435-2 in which they are identified as convex ring nails.
Once driven into place, these nails hold tightly against withdrawing forces and even forces tending to separate the planks or boards in which the nail may be embedded. In general the locking action derives from the fact that the material, usually wood or wallboard such as plasterboard, in which the nail is driven is somewhat elastic and is deflected outwardly by the nail as it is driven into place, the material springing back into the annular grooves defined between the adjacent ridges so that the steep flanks of the ridges cannot as easily deflect the material upon retraction of the nail. The result is a barb-like engagement of the nail in the material over the entire sawtooth profile of the length of the shaft or body provided with the ridges between the point and the head.
In practice, however, it is found that while the nails provided heretofore and in which the ridges all had crests of the same diameter so that they lie along an imaginary cylindrical surface coaxial with the nail, have been found to be satisfactory by and large, in many cases the springback action is less than fully effective so that the desired degree of antiextraction strength is not reached.